body { font-size: 20px; }
input { width: 30px; height: 30px; }
span { color: red; }
.clickMe { padding: 50px 50px; }
.clickMe { font-size: inherit; }
.wrapper {
    position: relative;
    display: inline-block; /* 必须是 inline-*，否则无法显示 popover */
}
.popover { padding: 10px 15px; margin-top: 10px; border: 1px solid red; position: absolute; left: 0; top: 100%; display: none; }
.popover::before { content: ''; border: 10px solid transparent; border-bottom-color: red; position: absolute; left: 50%; top: -20px; transform: translateX(-50%); }
.popover::after { content: ''; border: 10px solid transparent; border-bottom-color: white; margin-bottom: -1px; position: absolute; left: 50%; top: -19px; transform: translateX(-50%); }
.active { display: block; }